2.0 KV6 noise when hot.

Today I have driven my parents Rover 75 V6 manual for the first time for a while and after several 20 miles + journeys there were some intermittent grumbling/knocking noises coming from the engine bay. The idle was also ever so slightly rough. However, the car started fine at all times (hot and cold) and ran as smoothly as ever at all other times. When moving, or with a few 100 + revs applied the engine is fine. There is no loss of power and no lights have appeared on the dash. I checked the oil and water levels this afternoon and they all seem spot on.



The car had a new camshaft position sensor about 3 - 4 years ago and we had all three cam belts, tensioners, the water pump and the coolant changed in August this year.



I am aware of the VIS and manifold clogging issues but I would expect it to be worse when the engine is cold, rather than when hot (there is no issue whatsoever when the engine is cold).



The car is 14 years old, has FSH (serviced every year) and has covered 88,500 miles.



I did wonder if it could be related to any of the following:

- a worn engine mount. For a while I have noticed a perceived 'movement' when pulling away in first gear, especially when cold.

- air getting in where it shouldn't. When looking this afternoon I used the throttle linkage on the inlet to rev the engine slightly and there was a definite 'chuffing' noise coming from that area when the engine was revved. A similar noise was heard when I switched the engine off with the bonnet open. I suspect that much of this was taken apart when the belts were fitted. Could it be that there is a very minuscule air leak that gets larger with heat expansion as the engine warms up?



Other than the above, I don't really know what it could be.



I should also add that neither the VIS or the manifold system sound noisy when standing in front of the car with the bonnet open.



Any advice or ideas would be greatly received.



Thanks.

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