weird car noise, help

hng · 01-09-2007, 03:20 PM

OK, I don't know much about cars. I have a 1999 toyota 4 runner sr5 and lately i have noticed a thumping noise when I am stopped at red lights and such. When the car is in park or neutral, no noise. The noise is dull and deep, not metallic sounding, and is like every half second. I can't really tell if it's any faster with the gas on and it's not all that loud to begin with. Any ideas on what might be going on and should I take it to the mechanic?

tashier · 01-09-2007, 03:29 PM

Hmm, loud thumping noise. Are you completely stopped when it happens? U-joints come to mind since your 4-runner is rear wheel drive. Could possibly be your exhaust rattling around or even the motor / transmission moving around if one of the mounts is loose or bad. Pretty difficult to troubleshoot over the internet.

combiemaster · 01-09-2007, 03:44 PM

when you drive does you steering wheel move or pull to one side? have you notice any slugishness in the car recently or check engine light? Or just check under your car maybe you are drading a possume hehe

frankandmaura · 01-09-2007, 03:53 PM

Check the breaks too...could be a loose calliper.

hng · 01-09-2007, 04:03 PM

Wow, lot's of quick responses. Thanks guys. To answer some questions: haven't noticed any changes in driving or braking, no steering problems, and it's not a very loud noise. Only hear the noise at a complete stop in "drive". It seems to be more noticeable when the weather is cold outside. I have had my brakes worked on so I guess it could be that. The noise comes from the engine area so I doubt it is the exhaust.

frankandmaura · 01-09-2007, 04:07 PM

Oh, if it is only at a stop I guess it could be a loose belt or something rattling on the exhaust...I don't think you would hear anything from the brakes if you are stopped.

hng · 01-09-2007, 04:08 PM

I thought maybe it could be a fan, since it's a rythmic thumping sound.

tashier · 01-09-2007, 05:18 PM

Very tough call without hearing it. Could probably identify it pretty quickly hearing it in person.

Twitterbait · 01-09-2007, 06:41 PM

Also take a close look at any shrouds you have over and under the engine compartment. you may have a plastic one bumping with the rythim of the engine.

Phishnoob · 01-09-2007, 06:57 PM

A loose shroud would be a higher pitched sound almost bordering on tinny. Also, a belt driven component would be more whiny due most likely to a belt or a bearing.

Can you try just revving the throttle a couple of times and see if the pitch or sound intensity changes.

Also, as gently as you can try and get the car moving. Are there any noises or can you feel anything from the drivetrain. Try kicking it out of gear into neutral listening and feeling very closely. Are there any changes?

Try to be as objective as you can and take things on variable by variable and do this scientifically changing only one thing at a time.

Brake rotors, a heat shield, a belt driven accessory or other things mentioned in my opinion would not cause a thumping oscillating sound but more of a steady noise or whine.

Loverotties · 01-09-2007, 07:31 PM

U joint mite be going!

hng · 01-09-2007, 09:26 PM

OK, thanks for all the ideas. I will try to experiment tomorrow morning and see what I can find out.

Rippey · 01-11-2007, 04:47 PM

If its an electric fan, check to see if they have melted or warped. Rember to keep ur fingers away from it. If its a belt driven its not likely to be the fan (as long as its a metal fan). IMO plasitc fans are a joke. In the summer im always pulling the melted ones outa radiators. If the fan is melted also replace ur thermostat. Once the collent boils the thermastat is damaged almost always if not destroyed.

Rippey · 01-11-2007, 04:50 PM

Also is the engien running smooth, Shuddering at idle? Idle even and doesnt go up\down aloth on its own? Missfiring? You can tell that buy taking a dollar bill to the exusht if you hold it to the pipe (blocking the exhast with the bill) If it gets sucked itnto the tube the tube its missing. Usaly only works on a non rusted out exust system.