On my '88 XJ I've noticed a knocking noise when I'm stationary, in drive & of course on the brakes (say at traffic lights). I can feel a physical clunk along with the sound.

What would this be / how do I fix it?

Thanks in advance guys.

take a look at your exhaust it fits in a rubber fitting and it sometimes comes out and make a rattling noise

Where's the sound coming from? Can you elaborate on the sound details?
Mike

Is it just when the brakes are fully on? Or is it also when slowing down?

Mike - It sounds like it's coming from under my feet (I guess the driveshaft is there), it's a clunking noise that is repeats a couple of times per second.

I'll be putting in a new CPS on Thursday, when it's up in the air I'll have a friend stand on the brakes to replicate the problem & see what I can see.

Doobie - I'll listen more carefully as I'm slowing down but it's definitely more noticeable at a dead stop.

bsflipfrontflip - I'll check that on Thursday as well but presum I should here noises as I go over bumps in the road as well

Okay. it can be many things. but if it sounds like its under you, then it could very well be a drive line.

i had that probly and i could only hear it when i was slowing down or stopped

Do you know how to check the u-joints on the front driveshaft? And the slip joint? Odd that the sound would happen when stopped though... A clunk or metal to metal bind might lean us towards the front driveshaft. A metal tinging sound would lead us to the exhaust pipe.
I wonder how the motor mounts and transfer case mount is? Can you check those?
Mike

Ahhh, wait a minute... It's not the transfer case shift handle is it? When you hear the rattle can you stop it by putting your hand on the transfer case shift handle?
Mike

Mine made a squeek which was the TC handle.

OK so I turned the radio off & had a proper listen today.

It is definitely a clunking noise from underneath the front of the car - I also noticed it made the same noise on hard acceleration....when it's just cruising along the noise isn't there. I did not notice the noise as I was slowing down.

I had wondered if it was something like a u-joint. When I'm underneath her tomorrow I'll see if anything is obviously loose.

I'll see if it's the transfer case handle & I'll see if it happens in any other transfer case position....she's always been in 2wd since I got her.

I went for a short drive in part time 4wd & a short drive in full time 4wd high...the same noise occured in both settings.

I think it's u-joints in the driveshaft or Drivers side axel. Your original post threw me though when you said you could hear it when you weren't moving. Just remember to take a long screwdriver or prybar and really put some pressure on those u-joints to check them out. Disreguard the screwdriver or prybar comment if you already knew that...
mike

i think it sounds like your control arm bushings. probably lowers.

I've never had to check a u-joint before Mike so the tip is more than welcome. The noise only occurs (or at least noticeably) under hard acceleration or when in gear & on the brakes.

Caged - how would I check those? I'm sure there are all sorts of things wrong with this car, eventually I'll fix them all, but I think the noise sounds like it's coming from a rotating part.