I have a 2008 Envoy and noticed a chirping sound coming from the TPS Valve Stem a week and a half ago. I had just washed the vehicle at a car wash and shortly after I got home, I noticed the chirping sound coming from one of the TPS Valve Stems (it sounded like a cricket). We were leaving the next day for vacation so we decided to take my Wife's vehicle as we didn't want to come out of the airport when we got back to find the tire was flat. The chirping noise had stopped by the morning we left for vacation. When we got back 8 days later, I checked the tire pressure and it was the same as it was before we left. Would anyone know what caused the chirping noise? Thanks in advance!