Recently, I noticed what can only be described as a "ringing house phone" sound when the vehicle reaches a high enough RPM to shift into the next gear - it seems to occur at that peak moment when the automatic transmission is making the shift. Not sure if it's the engine, transmission, or something unrelated. It sounds like one of those "classic TV/movie" lower-toned phones - maybe a vibrating hollow metal-ish sound? It subsides once in the next gear, until it shifts up again. Oh, and it only seems to do it going up, not down, in gear. Any ideas?