I've been having this problem sporadically since new, which is now over three years.  For no discernible reason, the volume of the PDC beeps / noises is occasionally very loud - vastly louder than their normal volume.  Has anyone else experienced this?  Any known causes / solutions?

If using/moving the car quickly after startup you activate the sensors by getting near an obstacle, it can beep loud. If you wait for a second to get the infotainment to boot up, it should be normal in my experience.

Yep mine does this randomly from time to time too. Just another one of its quirks! 

Mine too.

Perhaps the explanation given by 386ka is correct. 

 

10 minutes ago, Giannis20 said:

Mine too.

Perhaps the explanation given by 386ka is correct. 

 

That explanation might account for some examples of this issue, but it doesn't account for what I experience - which is, usually when I have already driven a reasonable distance and am then parking.

Mine does this randomly too when parking up at home after a journey. I'm not knowingly doing anything different at the time. 

I think it might be the car's version of "Look out for the thing behind you...watch out behind...STOP!! YOU'RE GOING TO HIT IT!!!". That's usually just before it slams on the brakes so you think you have hit something!

I thought it got louder as you got closer to an object?

Yes mine has occasionally done this too, probably  4 or 5 times in the year i've had it.

Yes, the volume gets quite loud when really close to an obstacle.

8 hours ago, 386ka said:

Yes, the volume gets quite loud when really close to an obstacle.

It's not this.  When it happens (and like I say, it only happens occasionally), the moment I put the vehicle into reverse, regardless of how far away any objects are, the volume of the beeps is vastly louder than it normally is.