Today I noticed some weird stuff happening with my car:

-the interor lights briefly dim slightly every 2 seconds.
-there is a regular whining sound changing briefly pitch every 2 seconds. It's like a hiccup.
-about two seconds after turning off the engine there is a brief but quite loud sucking noise coming from somewhere under the hood that lasts for less than a second.

The whining sound is there both with the engine running (engine hot) and with the engine turned off and the key at position 2.

The sound comes from where the aux. waterpump is located and I'm pretty sure it's the pump itself making that noise because -with the engine off and key at position 2- I can feel the radiator vibrate and I can also feel the thick upper water hose pulsate with the same rhythm as the whining noise when pinching the hose with my hand.

Is this the auxiliary waterpump on its way out or is there something else going on?

And what's that sucking noise? A vacuum leak maybe?

I just had my coolant changed and waterpump and pullies replaced. AFAIK, my mechanic properly bled the engine afterwards. The engine idles fine, pulls as it always has and mileage is a decent 8.5L/100km >> 28mpg.

The car is a 2002 525iT with automatic transmission and 68,000 miles on the odo.

Any tips or info is well appreciated.