I had originally answered as a follow-up to another post on another forum about an odd noise like a oooooooh singing sound at 2200 - 2800 rpms in any gear that could be heard coming through the instrument cluster. The sound made driving the car in any traffic horrible. No one else on this forum seemed to have the same problem as I was having or ever bothered to mention it. It could be heard over music on the radio. I thougnt that I would also post it here just in case someone also had the problem and now could go to their dealer with some info.I was very persistent to get this solved. I bought the car on March 31 and was at the dealership for the problem the first time April 7. It was resolved on June 11.
If anyone is wondering why I never heard the sound when I test drove the car, the sound occurs only when the engine is warm and only at 2200-2800 rpms in any gear. I drove the car on a highway and only for about 1.5 miles.The problem has been fixed by a GM Field Engineer named Brett.
Although another post on that thread indicated that the sound was a harmonic from water flowing through the engine and there was NO fix possible, the FE worked to solve it.He worked with a tech from my dealership. The FE was in contact with other engineers at GM and after the sound transferer was found to be the heater core , many steps were taken to eliminate the response. The first suggestion was to remove the tubing that goes to the heater core from the front of the engine back to the firewall connection. Apparently the GM engineers felt that the aluminum tube was restrictive and the place where another pipe was welded on was attached , the attached piece extended too far into the space and water flowing passed it set up a noise. So the aluminum piece was reamed out to open it more and the slight extension of the affixed pipe was ground away to make it a smooth pipe. After which the rubber hoses were re-attached to the firewall , the pipe reclamped in place, and the last set of hoses were attached to the water pump.(Long and tedious process of almost 3 hours start to finish.......drain coolant, remove shroud, clamps, remove battery , etc. ) The fix didn't work!
Finally the FE tried just to lengthen the hose that comes from the water pump and connects to the aluminum pipe. I think he figured that the loop in the hose might change the harmonic.He had the tech, Matt replace the test hose with regular black heater hose the following week. Although there is a slight crimp in the hose, the fix works. I am still testing the fix and will wait til fall to see if the crimp in the hose will affect getting heat inside the car in cold weather. I waited to post this because I really wanted to be sure that the sound was gone. I really is! The harmonic sound from the engine is probably still there but is not being transfered to anything else that sends a noise that can be heard.Possibly there will be a bulletin on this problem so that other dealers can solve the problem if it ever comes up.
The aluminum tubes are not involved in the harmonics as determined by trial and error. The harmonics are created in the water passages of the engine. Once the thermostat opens the harmonics travel through the coolant to the heater core which amplifies the sound. The tubes themselves are NOT the sounding board. The sound is transmitted by the coolant. The audible range is in the 2000-3000rpm range of the engine.1. Source: engine Cannot alter