Hi all, I've been hearing this "whirring" noise after we flush the 1st floor (main) toilet when the refill valve is refilling the toilet. The noise ceases once the tank has filled. Assuming that it could be anywhere from the shutoff valve to the refill valve, I replaced both. Unfortunately, that did not solve the problem. What's interesting or weird is that the noise can be triggered from the two upstairs (2nd floor) toilets as well although it seems to be the loudest and consistent from the 1st floor bathroom. I thought it was only isolated to the 1st floor toilet, but I must admit that I did hear that same "whirring" noise after the 2nd floor toilet was flushed even though with those toilets I can't seem to replicate as consistently as the original 1st floor toilet. I had a feeling it might not be the shutoff valve or refill valve that was the culprit after noticing that even on occasions and to a lesser degree (noise wise), the 2nd floor toilets were also triggering this noise. But it definitely is the loudest and most consistent from the 1st floor toilet. Please help! What could be causing this all of a sudden? Thanks in advance.