Hello,

I noticed today an intermittent hum or tone coming from the radiator. It is barely audible in the cabin, it almost sounds like a fuel pump would. I isolated the location by using an automotive stethoscope. When I put the metal end of the stethoscope on the top of the radiator the hum / tone is very loud and clear (it is an intermittent medium hum, not whiny, sound).

I recently drained the coolant to replace the thermostat. I reused the old coolant (filtered). I opened the reservoir cap but that didn't have any impact on the hum.

The hum / tone almost has the sound of a power steering pump when turning your steering wheel, to help you imagine it in your mind. The radiator also cools the transmission fluid (auto transmission).

Any ideas based on past experiences?

Thanks, Joe