BMW 528 exhaust / cat hot tick problem

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Thu 8 Sep 2005 11:19
BMW 528 exhaust / cat hot tick problem - green machine
My 1999 BMW 528 has particularly distinct hot ticking exhaust noise.

This happens both once the engine is off for some considerable time (20 minutes), but also there's audible hot ticking noise when the engine is idling, and it's noticeable when driving with the window open in a confined area such as a car park, or driving alongside a wall.

I've had a close look underneath and referred to the recently introduced Haynes manual for the car. The exhaust appears to be one complete system, all the brackets and mountings seem to be in good order, as does the exhaust itself.

The only part of the exhaust which seems to be the likely culprit for the ticking noise are the catalytic converters. They have a shield on each cat which seems to be a different metal to the exhaust, they are welded to the exhaust on the leading edge, but not at the back of the shield. They also seem to have some packing material inside the shield which can be seen through some holes in the shield intended to let heat escape.

I've recently put the car through the MOT and there were no problems in the emissions testing, so I assume the cat's are all in order.

Any one else come across this exhaust hot tick, I know most cars have some exhaust and engine hot tick, but being able to hear it over the engine whilst it is running seems unusual to me?
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