MYSTERY THAPPING RATTLE SOUND
Asked by Guru9L582D Aug 20, 2021 at 10:22 AM about the 2011 Kia Sorento Base
Question type: Maintenance & Repair
I have a loud engine "thapping" like rattle sound at low RPM (<1500 RPM) only when the AC is running and the vehicle is in gear. We've eliminated the most obvious causes: replaced the AC compressor, checked all the pulleys (and replaced serpentine belt), and replaced the power steering pump with no change to the sound. If I turn off the AC or increase the RPM above 1500 the sound goes away. No change when the vehicle is moving. It has stumped three different mechanics. What else could it possibly be (i.e. rack and pinion, water pump)?
4 Answers
Guru9LYVJX answered 3 years ago
Disconnect the drive belt and see if the noise goes away. Rack and pinion only should make noise while turning the steering wheel. Is it a heat shield or loose exhaust? It's not a lifter tapping either? Stethoscope can help greatly. Also check by the flywheel and starter to see if any obvious noises.
Guru9L582D answered 3 years ago
Few updates based on comments: I removed the serpentine belt and ran the vehicle. There was no noise with the belt off. I rotated all the pulleys and they felt smooth. I put the belt back on and the noise came back. I used a stethoscope, but could not locate the source. The sound travels through the AC and power steering pump and the rest only sound like normal movement. The sound doesn't change at all when I move the steering wheel, so I think you're right that it isn't the rack and pinion. The heat shield is tight, but I didn't consider moving the exhaust, I'll give that a try. As far as a bad idler wheel/tensioner, the stethoscope didn't indicate any noise from there. Do they ever go bad in any way except failed bearings?
Guru9LY3CC answered 3 years ago
The Bearings do get louder when they do wear. If there is a worn or bad spot in the bearings of the idler or tensioner can cause them as well. When checking sound with a stethoscope you got to listen closely to notice any sound changes as well. Different RPM can change noises as well.
