For the last few months car has had a knocking sound (Sounds like something hitting / vibrating against the bodywork)whenever I start the engine up or if I accelerate in 1st 2nd and 3rd gear. Knock seems to come from around the manifold area.
Noise does not happen if I rev the car whilst it is standing. Same revs and moving produces a knocking sound.
The knocking sound can only be heard from inside the car. Shaking exhaust does not replicate sound.
Any ideas, it is driving me mad as all I can hear on the way to work is this knock everytime I accelerate.
I can't replicate the sound any other way. Possibly thought it was engine mounting but doesn't make noise when revving stationary.
It could still be the exhaust, sometimes they knock on things further away than you expect. You have to get underneath and really violently push and pull. The engine will move a fair bit under the conditions you describe and so will the exhaust.
I also wouldn't expect reving while stationary to move the engine much at all compared to when its under load
For the engine mount possibility:
If you can't easily see the engine mounts to check them you could open the bonnet and start the engine by reaching through the window while standing outside the car and see if the engine moves much (double checking its in neutral before doing this). Or if you can see the engine from in the car with the bonnet up you could briefly try to drive the car forwards with the handbrake on or get someone else to while you stand out side to watch the engine for excessive movement (I'm not sure what would be classed as excessive movement though?).
Similarly for the exhaust if you look under the car while starting it you may see how much the exhaust moves and get some idea of the clearance it needs.
When you say vibration do you mean it knocks when you first push the accelerator and then you hear the vibrating all the time your accelerating?
It knocks a second after the accelerator is pressed. Just as if there is something moving (I have checked spare tyre, jack etc just in case) under a fair load. If I pull away slowly it does not knock. It always knocks when the engine is started.
The knock is usually a single knock, sometimes two.
When starting the engine there seems a bit of movement in the mounting, but I can't compare it to any other Avensis. It moves more than my VR6 golf but I would eguess that it is ok. Not very easy to look at the mounting.
When the exhaust is shaken underneath, there is no noise. I have just checked the movement underneath while starting and there is not as much movement as shaking it.
My last try was to get the exhaust taken off then out back on again. A few places have told me that they don't want to do this (presumably as they aren't making much money out of it.)
I can't recreate the knock any other way which is the annoying part as the knock can't be heard outside the car, only inside.