I've recently noticed one of the components in my HTPC making two weird sounds every once in a while, probably 2-3x a week and sometimes twice in a row: A 1sec beep followed by a very audible clack - BweeeepClack!
Due to the clack - Which I assume is coming from a Solenoid - I'd say the culprit being either the ASUS ROG Thor 850P or the ASUS ROG RYUJIN 360 but with me usually situated 3m away I've never been able to listen to where exactly it is coming from, I can only guess. There's also other stuff cramped in the tower like the PSU from a Kinect 2.0 and a 5-Port Switch but If I really had to put my money on it, I'd guess it being the Thor.
Besides the two noises nothing else happens - The system isn't crashing, I'm not getting any error messages, etc...
Whats the rest of your specs? AIOS can be noisy just from improper orientation and getting air in the pump (cavitating) or stuck in the inlet of the rad that would be more gurgling sound. Beep and clacks, especially lound ones would bother me. Beeps are telling you something isnt right then the clack behind it sounds like a reaction to the beep and if I had to choose between the two you listed Id be more inclined to call it the PSU. Hoping the clacking isnt component component failure as there arent any solenoids involved with either. A capaitor in the PSU can pop. Any stank coming out?
The AIO is pretty much unnoticeable as of now and hasn't changed since I installed it - Radiator at the top with the Pump/Cooler below it. If the clacking were popping Capacitors, I'd probably not be writing from this PC anymore considering how often it now has happened over the past few weeks.
There's no smell either. Really just the short ( kinda sickly sounding ) bweep followed by the clack - Whenever I rush to the case to open it in case a second event happens for me to pinpoint the location in the case the THOR OLED Display usually shows a load between 80-150W - Practically nothing.