High rpm exhaust buzz/rattle

[simonc1984]

Hi All , i dont tend to need the forums that much as honestly the car doesnt go wrong all that often , i have a 2004 v70 2.4 non turbo , around a month ago i had an intense rattle from the catalytic converter and subsequently this was diagnosed as cat failure so i had a new one put on which is an aftermarket brand but not sure which brand as a few were mentioned at first , a oem volvo one was way out of my range as things have become quite tight in the last couple of months , anyhow things are ok until i am accelerating past between 2800-3100rpm and i get like a shakey buzzing almost rattley noise thats coming from where the new cat is , before an after that rev range it is quiet , i have been back to the garage and they are saying there is nothing they can find wrong and it certainly wouldnt be the new cat , i have also been under and cant see anything out of the ordinary , the new cat was 600 quid before labour costs and they are saying i most likely need to pay the cost of a new cat again if it needs replacing again , before i get robbed again i was wanting to ask if there was any ideas or things i could try before , thanks in advance , simon

[stuart bowes]

before worrying about costs I would take a good look at heat shields, or possible a bracket or something they fitted is close enough to vibrate against bodywork at certain frequencies

[simonc1984]

Originally Posted by stuart bowes

before worrying about costs I would take a good look at heat shields, or possible a bracket or something they fitted is close enough to vibrate against bodywork at certain frequencies

Hi , thanks for your reply , ill have another look in the morning , couldnt see anything at first glance , cheers

[Georgeandkira]

+1 on inspection. Even thoughtful mechanics/shops perform Gerry rigs on thin sheet metal ancillaries.
Also, have you looked at the rear resonator box? Mine ('02) rotted out thoroughly.

How many miles are on your '04? Maybe give the engine mounts a look too.
FYI: The mount beneath the front crank pulley requires raising the FL corner, removing that wheel, removing 2 10mm sheet metal nuts and folding the fender liner back. It'll be right there. The rubber collapses and an engine speed related buzz is the result. I've changed them in two V70's.

[simonc1984]

Originally Posted by Georgeandkira

+1 on inspection. Even thoughtful mechanics/shops perform Gerry rigs on thin sheet metal ancillaries.
Also, have you looked at the rear resonator box? Mine ('02) rotted out thoroughly.

How many miles are on your '04? Maybe give the engine mounts a look too.
FYI: The mount beneath the front crank pulley requires raising the FL corner, removing that wheel, removing 2 10mm sheet metal nuts and folding the fender liner back. It'll be right there. The rubber collapses and an engine speed related buzz is the result. I've changed them in two V70's.

Hi , thanks for getting back , the rest of the exhaust is in great shape plus the noise in question wasnt there before the cat replacement so it must be something thats occured during this repair , the car is currently on 119000 miles , the front , rear and side lower mounts have been done , next in line is the top one and the gearbox mount at the front , i`m going to have a lay down under it in the coming days when i get 30 minutes to myself , thanks for your advice , simon