Crazy toilet assistance please!
 

A recently installed toilet is giving us fits. It has been removed twice and re-installed to no avail. It makes an odd whistling/wheezing/hard-to-describe sound when it is flushed. Then several days later, we noticed that the second toilet in the other bathroom has a "wave" when the first toilet is flushed. (They are back to back on either side of the same wall.) Then realized that the whistling toilet also has a wave when the second toilet is flushed. This seems bad, very bad. The installed toilet is the same as the other 2 toilets in the house, and we haven't had any trouble with them. Any ideas or suggestions would be great appreciated! Thank you!

Over time the flush valves can fail or become plugged up with minerals.
It's a simple 10 min. fix to change one.
When they do plug up they can start to change sounds.
http://www.fluidmasterpro.com/

Just a guess, for there to be sound there needs to be vibration, if the incoming water line is vibrating because of a bad flush valve it may be just causing the water in the other bowl to also vibrate causing the wave.