Generally the whole of the cabin shakes a little when I'm at idle. It's only started happening since I fitted a second hand back box and centre section to the car which were kind of ball ache to fit, nothing lined up well at all.

When I rev past idle, the vibrating goes away and this doesn't happen anywhere else in the rev range. I've double checked that none of my exhaust is touching the car itself, nothing is. But when I touch the boot at idle, I can feel it vibrating even though I can't see how? Is it something to do with resonance, if so how can I alter it? Is it something to do with the rubbers holding the exhaust on?

Also, I have some blow holes, would they be the reason it only happens at idle? Then when the revs increase, the gases flow better and the blow holes arent such a problem? This is so annoying, I always have problems with these shitty polo exhausts grr

If it's leaking then this isn't going to help. Did you use assembly paste when you put it on, like Holts Firegum? This helps seal up little leaks and helps things slide together better.

The fit of some of the cheap exhausts are shocking. I went for a Leistritz back box this time around...OEM and it shows!

Is it the correct bore size, or is it some 'performance' malarkey?

If there's not enough back-pressure your gasflow can be unstable, causing vibration and reduced efficiency.

No two exhausts are absolutely identical (neither are engines) in the way they flow. So it can be a bit hit'n'miss with getting one to hold the flow smoothly, with minimum restriction. And a touch of plain old fashioned luck thrown in.

Add in problems such as damage, leaks, bodge repairs, lumps of firegum paste inside etc etc and you've got no chance of clean-flowing smoothness.

Exhaust U-bolt rattling on the floorpan?

It's a standard exhaust chaps. I've checked and double-checked nothing is catching on the body, it's not. It's literally just at idle, when I increase the revs even to like 1000 the sound goes away. If something was touching, surely the sound would still be there then?

I've just pasted all the holes aswell so there are no leaks, and it didn't make a difference. I also tried removing some of the hangers and it made no difference.

It's really rather annoying, and I have no other ideas what it could be. If it was engine mounts, wouldn't it be noticable at other rpms?

Mikey I hope you are right, and it's just a bad mix of differing pipe diameters and restrictions, at least then my mind could be at rest a little lol.

I had savage vibration at idle which then went on to cause mmy exhaust to rattle on pullaway, on further inspection my gearbox mount (under the battery) was as soft as putty so after repairing that the vibration was gone but it had caused my U-bolts on the exhaust to come undone and rattle massively.

I had savage vibration at idle which then went on to cause mmy exhaust to rattle on pullaway, on further inspection my gearbox mount (under the battery) was as soft as putty so after repairing that the vibration was gone but it had caused my U-bolts on the exhaust to come undone and rattle massively.

Interesting dude. I'll give that a look, would make sense.. did it still vibrate once you picked the revs up? Cause I imagine it would if there was a mount gone..

No it didn't! It baffled me for a while until I checked it. The car would feel normal apart from a little jerky when coming off the accelerator but as soon as the revs dropped to 900rpm at standstill my whole dash would be shaking.