Wife's Fabia Mpi has developed an odd knocking from underneath.

It stops at speeds above about 50mph.

It doesn't directly correlate to hitting bumps or going round corners but seems to be more related to general vibrations.

It's also quite a 'light' noise as opposed to a clonk or thud of suspension bushes. Almost like metal or plastic vibrating.

Having driven it last night, I don't thinks it's steering or suspension related (but I could be wrong) and doesn't sound like a serious / expensive noise.

Anyone got any suggestions as to what to check that might be causing it?

Thanks.

check the plastic under tray, which is under the engine, have had mine on fabia, octavia and roomster ping a fixing or two and that produces either a scraping sound on high speed roads or tapping / light banging on low speed roads

Check the exhaust and it's mountings.

Is the noise loudest when coming off the throttle? If so, then check the pendulum mount at the rear of the engine.

I'd say drop links if it was me - doesn't directly affect handling adversely but does produce a kind of knocking noise that does seem to die down at higher speeds...

The shout for engine cover is a good one too, as is exhaust mountings.

Been under the car all morning and found...

Nothing.

Engine cover not fitted. Sorry.

Neither was the engine under tray.

Exhaust mountings was my first check. All fine.

Did find leaking oil from the engine temp sensor (I think that's what it is) and perished rear bump stops... And a broken metal bracket the holds the coolant pipe by the sump (the pipe Chris Coates told me to look at yesterday - pipe looks OK though.)

It's not a loud noise - it more a vibrating / rattling noise.

The noise is not related to accelerating / decelerating or directly to road speed (other than it disappears over 50mph).

It's also not directly related to hitting any bumps on either side of the car.

Thanks for all the suggestions - Please keep them coming. I have until Monday then the wife wants it booked into a garage for this and the oil leak / mayo in coolant problems as well.

Ok. If it's a rattling...

...Are you sure it's not something inside the cabin?

Most common rattles are in/around the centre console. Namely the seatbelt clips rattling against the centre console or the handbrake cables/handle rattling...

Join the club m8

Pretty sure it's not inside the cabin as I had a good listen around while the wife was driving back yesterday.

It also feels like the vibration is coming from under the vehicle through the floor pan.

With one front corner jacked up, I tried wobbling & turning the front wheels to check wheel bearings, etc. and found that there seems to be quite a lot of play and nose coming from the differential under the engine. (I think thats what it is - its where the two drive shafts meet).

Turning the wheel back and forth with my other hand on the 'differential' and I can feel quite a bit of 'knocking' in there.

Could this be it? Should there be much free play in the differential? Should I get a knocking there at all?

There shouldn't be a massive amount of play...

If you're hearing what I can only explain as a droning sound at lower speeds that goes away at higher speeds... Then suspect wheel bearing or like you noted - driveshaft/diff.

Not a droning noise. Sorry. There is rather too much play in the diff though.

Will have another look around (and inside) to see what else I can find.

Look at the ARB bushes just to make sure it isn't them!

Had a look at and fiddle with the bushes, but couldn't see anything. Doesn't sound like that sort of noise either.

Will have another look though and focus on the ARB bushes you suggest.

I have the same prob with a knocking noise and struggling to find the culprit

The old ARB had a plastic sleeve which was glued to the ARB which also had the end stop built in.......over time rust un-glues the plastic sleeve from the ARB and although the metal saddle clamp will be clamping the rubber bush and and looks OK the plastic sleeve moves and so does the ARB itself.......so it slides from drivers side to passenger side.......needs thicker ARB bushs to clamp it...unless you do spirited driving then defo replace the whole ARB with the later spec one which had built in metal end stops to stop it sliding!!

AS for the Mayo.......my mates car had the same problems (same engine)........also his had the common thermostsat failure....so new thermstat and housing fitted after a hot flush of the coolant system and clean of the expansion tank etc......then refill with the PROPER VAG PINK coolant!!!.........1 year on and still all OK and no mayo!!!!!!

The old ARB had a plastic sleeve which was glued to the ARB which also had the end stop built in.......over time rust un-glues the plastic sleeve from the ARB and although the metal saddle clamp will be clamping the rubber bush and and looks OK the plastic sleeve moves and so does the ARB itself.......so it slides from drivers side to passenger side.......needs thicker ARB bushs to clamp it...unless you do spirited driving then defo replace the whole ARB with the later spec one which had built in metal end stops to stop it sliding!!

This sounds like it would be a serious knocking that would be more noticeable while changing direction?

My 'rattle' occurs frequently and randomly and is a more than a few obvious 'clunks'.

AS for the Mayo.......my mates car had the same problems (same engine)........also his had the common thermostsat failure....so new thermstat and housing fitted after a hot flush of the coolant system and clean of the expansion tank etc......then refill with the PROPER VAG PINK coolant!!!.........1 year on and still all OK and no mayo!!!!!!

Think I might try that before I start taking the engine apart. Even though I've got all the bits to replace the head cylinder and gaskets...

This sounds like it would be a serious knocking that would be more noticeable while changing direction?

NOPE!!!!!!!!...........as when the suspension is loaded the bar tightens up against the bushes......only rattled in a straight line at slow speeds when there was no twist load or force load on it........best to rule it out anyway!!

OK. I shall take a look as soon as I can.

Thanks.

The old ARB had a plastic sleeve which was glued to the ARB which also had the end stop built in.......over time rust un-glues the plastic sleeve from the ARB and although the metal saddle clamp will be clamping the rubber bush and and looks OK the plastic sleeve moves and so does the ARB itself.......so it slides from drivers side to passenger side.......needs thicker ARB bushs to clamp it...unless you do spirited driving then defo replace the whole ARB with the later spec one which had built in metal end stops to stop it sliding!!

AS for the Mayo.......my mates car had the same problems (same engine)........also his had the common thermostsat failure....so new thermstat and housing fitted after a hot flush of the coolant system and clean of the expansion tank etc......then refill with the PROPER VAG PINK coolant!!!.........1 year on and still all OK and no mayo!!!!!!

I will check my arb for the collars, I replaced my arb bushes with powerflex ones so I thought my arb was fine. Any pics of these things

Check the bonnet for play that was my culprit I put some tape on lock and bonnet has no play when locked, worth a try

Ste j - I'll take a look to rule it out.

Hope to have a look at the ARB bushes this afternoon if it doesn't rain...

What do these arb collars look like folk?

Drove the car for the first time in a couple of weeks and it seems worse than previously - more of a rattly / knocking noise now.

Chris Coates wins the prize! Turns out to be the anti roll bar drop link!

Looks pretty straight forward to change. Do I need to be aware of anything that will affect the steering geometry or wheel alignment?

Won't affect anything just replace it