We thought it was the  backbox initially but its not, I have a weird resonating sound which goes through the car at approx 2200rpm, above or below this is fine, it hasnt got louder since it started approx a year ago but I have lived with it.

 

We also slipped off the auxiliary belt but this has made no difference, also the same without climate engaged/disengaged.

 

Maybe this video will help! 

 

https://youtu.be/HbnPHfz6uu4

 

Thanks for any suggestions

Edited 4 September, 201510 yr by Liverpool-Lad

Can't offer you many suggestions but I can offer my sympathy, my Saab does something very similar at the same rpm funnily enough. Mine sounds like exhaust resonance, when I was under it recently I did spot that it has poly subframe bushes, and my exhaust moves quite a lot, so I'm thinking it's both.

Are all your exhaust mounts ok? Is the flexi alright?

Yes this sounds very similar but the exhaust has been ruled out.  The actual shell/engine of the car cab be observed to vibrate.  I think the exhaust is acting almost as a tuning fork hence why the exhaust was thought to be suspect!!

Edited 4 September, 201510 yr by Liverpool-Lad

The cambelt/pump is due soon so they will look at it in closer detail then whilst they have it up in the air.  Interesting on the poly bushes too.  All heatshields and OK and exhaust seems fine.

Yeah get them to have a closer exam. It's funny how these things happen at a particular frequency/loading, I think/hope with mine it's a combination of a few things happening at once: part throttle, early boost, usually uphill, engine movement, exhaust movement and bushes. Soon as I press throttle more or lift it stops. Would have thought if it's turbo issue it would happen at higher boost. Anyway this doesn't really help you much, it could be either something daft or a similar combination. I've not located my vibration yet but as it's only at that loading I'm not overly concerned. I can't recreate mine when stationary as I think it's to do with loading and movement.

At least I have a shiny new backbox - £200 :(

Ouch...

Mine does the same at about the same revs. Is yours noticeable while driving? I don't think it's a rattling heat shield or anything like that - I suspect it's from inside the exhaust. My car is on 134k now and still on the original exhaust.

 

I think the best way to diagnose it would be to put it on a ramp and hold it at the revs where the noise occurs, then have someone under the car trying to feel/hear where it's coming from. If you find it please let me know, but if you can't I wouldn't worry about it. Joys of owning an old car

Isnt this odd...mines on 97k now.  The suspect was the backbox but at that rpm the actual engine and car start to vibrate a bit so the exhaust was ruled out. although when you suggested we did look under the car and I could hear the sound through the cat and middle box - whether these are acting as resonators amplifying the sound or are the actual culprits is a mystery so far!

If you figure it out too let me know as it can be really annoying!!

Happens when stone cold also!

Cats have been known to rattle under load, also is the centre bracket fully secure to the centre pipe or has one or two of the welds come adrift?.

Centre bracket is a-ok and has been welded recently.  Would the cat cause the engine to vibrate and also the shell?

 

It feels as if the engine is somehow very slightly out of balance at that rpm.  Ive also been suggested the crank pulley as Im pretty sure they may have a rubber component?

Edited 5 September, 201510 yr by Liverpool-Lad

Would not have thought the cat could cause that, pulley may be a possible cause, but to be honest I would be looking for power unit mis-alignment due to worn engine mountings or for exhaust rubbers coming to the twilight of their days.

 

Car manufacturers put a lot of effort to reduce NVH (Noise Vibration Harshness), which tends to equate to rubber mounting just about everything that moves, so a little extra movement in a mount rubber may make quite a noticeable difference.

 

Are any cables connected to the car like gear change cables going to ground or poorly grommeted at all?

 

Just a thought, when the exhaust bracket was welded, it was centralised in the cross member that runs under it afterwards?, as it moves around an awful lot in there as standard.

Bump in case anyone else has seen this problem.  A few people seem to report it after googling but no definitive answer.

 

The actual engine vibrates and the shell slightly so Im thinking more engine related as the source of the vibration than cables etc.

 

Im wondering if engine/dogbone mount could cause it?  I know also the crank pulley is a 'damper' of sorts with a rubber core

 

The car is in for a full cambelt/waterpump swap next week so Im hoping they can take a closer look at it then.

 

Cheers

Edited 3 October, 201510 yr by Liverpool-Lad

Id start with engine and gearbox mounts.

Bump

Any news on this dude? My Saab still does it, it remains a mystery...

None. Im wondering if its the subframe mounts?  At certain speeds/roads I feel sort of a low rumbling/slight vibration under the drivers side floorpan.

 

It is still there when stationary also.

Edited 4 November, 201510 yr by Liverpool-Lad

Mine does this also! It is Vibra-Technics dog bone as well as 3" downpipe/2.75" Magnex related. My vibration comes in when on overrun and is most noticeable at 3000rpm, which is about 70mph in 5th. The whole car resonates at that point and especially the front passenger seat. Interesting when a girl is sat in it and I lift off at dual carriageway/motorway speeds...

Does it also do it when idling and revving like the video?

I still don't know what's causing it.

 

As I said before I think the best way to track it down will be to have the car on a ramp with someone under the car poking around while someone else is in the car holding the revs.

Mine does it but mine is running rough. Changing the ecu. Suspected ecu, throttle body/sensor and crank breather, injectors (over fuelling).

Rough running is more likely than a bush.

This is the odd thing though, bar that odd noise the engine has no fault codes and drives perfectly fine.  Bags of power and no other issues - just this annoyance at 2200rpm

I'm on a mad spree of telling everyone to try a fuel system cleaner and see if it fixes anything. "Drive clean" is what i used and all seems good. See my "wierd firing when hot" thread.