Often, when I park the car and it is idling...there is a knocking sound that comes and goes from my engine. It seems to come when something automatically turns on for a few seconds and then shuts off again. It sounds like a knocking, or steady rattling. It has just recently happened, and only happens when idling. I have replaced the water pump about 25,000 miles ago. Any ideas?

A co-worker of mine had the same thing on his 94 325 and he still hasnt had it looked at. It has to be a year or so since it started happening. Cant be that vital but you never know.

How many miles on the engine? It could be a lifter marginally operating. Could possibly be due to low oil pressure at idle.

You mention that it sounds like something is turning on at this time. How about the AC compressor? Try opening the hood and get your ear closer to try to pinpoint the source.

I'd check your oil. It's probably a hydraulic lifter making noise because it's not getting enough oil.

It's got plenty of oil, and it doesn't do it all the time when idling. Only for a few seconds...and not every time it idles either. When it does happen though, it's loud and does NOT sound right! I have about 125,000 miles on the engine. It runs strong and doesn't burn any oil between changes.

FWIW my stock flywheel rattles occasionally at idle when the a/c compressor kicks in. Is your a/c on or off when this happens?

It is probably the AC. I can remember him having issues in the summer which is when he runs the AC. I am just throwing out ideas here....

Makes sense. By the way, BMWDRIVEN, your car is gorgeous. I don't see too many like that around.

It gotta be the ac compressor.....that happened to me over the summer and eventually it's gotten so bad that everytime I hit the "cold" switch on the ac the sounds come cuz of the compressor. I went to the stealer to get a quote and they told me around $1500 including labor.......I am screwed :(

Not sure if it is when the ac kicks in or not...I'll have to pay attention. Thanks for all the info!

its yoru catalytic converter vibrating against the passengerside wall, get under and chekc it out

just push the cat side to side youll see it and hear it, ill post a pics of what i did to fix it tommarow

I hear that sound only when i hit a/c button with high speed about 80mph, so do you guy think something wrong with A/C compresor or something else. Thanks in advances.

I hear that sound only when i hit a/c button with high speed about 80mph, so do you guy think something wrong with A/C compresor or something else. Thanks in advances.

grasping at straws guys.

Ben first of all, is it when the a/c is on? secondly, you need to put your ear under the hood and see where the sound is coming from. Third how is your idle when this happens (does it drop or surge)?

Most likely it could be something to do w/ the A/C fan, the A/C or a/c belts as those are the most common sounds from the engine. It could also be the engine idle dropping from the increased strain of the a/c compressor causing a knock.

But again, open the hood and tell us where the sound is coming from.

Could you be more specific as to the location of the noise and what the noise is? I had a "ticking" coming from somewhere in the engine a little bit in front of the driver. If that's your noise, it's just a .75 bushing. In fact I had it diagnosed and fixed at Capital Cities which is in your area.

I have a noise too, though I don't know if it's the same thing. When I am sitting at a light, I hear a very light knocking noise coming from the other side of the of the radio/blower. When I opened the hood the noise sounded as though it was coming from underneath the black grill that is right next to the fromt window.

I had my inspection 1 done last week. B4 the inspection, the noise only occurred when I had the blower on, but only at idle, now it occurs all the time, but only at idle.

I have a feeling it has something to do with the HVAC system. I hope this is normal. I've never actually paid atrtention b4. I usually have the radio on, and you can't hear it when the radio is on.

I forgot to mention, the knocking sound occurs once every 4 to 5 seconds.

David,
Mine was more of a tick, tick, tick. About 60+ per second. It was intermittment, but I could only hear it when the car was not moving.

Originally posted by msellman
David,
Mine was more of a tick, tick, tick. About 60+ per second. It was intermittment, but I could only hear it when the car was not moving.

Michael,

The noise I'm hearing is more pronounced, thus I'd describe it as a very light knocking noise. You're guaranteed to hear my noise while the car is idling. I wish I knew what it was and if it's normal.

Did you ever diagnose the cause of your ticking? What was it from?

Take it easy.

replacing both belts worked for me, only cost like $35

My problem was a 75 cent bushing. To answer your question, no noise is normal if it didn't happen from the day you got the car.

Originally posted by IlllIlI
replacing both belts worked for me, only cost like $35

How hard is it to do that procedure? I know I'd need a torque wrench, since I don't own one yet, but what else would I need? I don't own the Haynes or Bentley manuals. Or should I just take to dealer.