At first I thought this may just be the noise floor of your receiver. But then I began to wonder
-is it a constant level of nose?
-is it volume dependent?
My first thought if the level is constant, is that some of the windings in the laminated power transformer core becoming "de-laminated" with age and vibrate causing a hum as power is transferred across it. Usually you will hear this coming from the chassis of the affected component. But the way you describe the "puh puh puh" - in my head makes an undulating sound. Which I correlate with the familiar 60Hz main power cycle.
If it's volume dependent then it may be something feeding into your receiver that's causing the noise, whether it be 60hz mains hum from single ended cables being in proximity to a magnetic field source, or something of the like.
Components can operate for a long time even when the power transformer begins to hum, due to age or other factors like QC or abuse. I don't think it's indicative of a catastrophic issue. But it may be a good time to get in there and have a look for yourself. If you aren't so technically inclined a reputable repair shop should be able to tell you exactly what's wrong with it. If you want to keep the unit it may be time to have the power supply caps checked and changed if out of spec or leaking, along with checking and possibly replacing the power transformer for the spurious tones you're hearing at the speaker.
As I'm sure you know, start small and slow and then move onto bigger potential issues during troubleshooting. Sometimes the silliest thing can make a big difference.
Cheers!
