Vsx-815 Tuner Will Not Tune Lower Stations On The Band, Until 20 Minute Warmup?

The question says it all, when the receiver is first turned on only the highest stations such as 106.3 will play. Lower stations, such as 91.5 will not play and just a weird bah-bah-bah sound is heard. Even a station such as 101.1 will not play, at first. Same nonsense noise. BUT as the receiver warms up, Mhz by Mhz, lower and lower stations become perfectly audible. First 103.x, then a couple minutes later 101.1, then down to 97.3, and so on. It takes over 20 minutes before stations at the lowest end of the band become playable. In fact, you can "sit" at a frequency thats about to appear and after a while it will come in. The bah-bah-bah switches to a hum and distortion, and then finally tunes it.Can anyone explain what the theory may be that causes this, some oscillator component thats failing but responds better as it warms up? I assume the fix is to replace the tuner assembly, if one can be found. Or just be very patient! :-)