The tweeter of my mackie srm 450 V2 makes a quite loud noise (humm). this nois was there right from the beginning, and mackie told me, that this was usual....the older 450´s did not make this kind of noise. you don´t hear it, when playing with the band, but when I play my e-piano over a 450 and sit next to the box (1meter), it is really annoying. I guess, that´s the price of "made in china", isn´t it.... I´m gonna sell my mackies and get me a system from dynacord or hk audio!

The latest 450v2 include this metal portion 1 to isolate AC lines over IC's, metal part 2 is include in all versions, some technician remove them and that creates more hum at idle levels, by having both the latest 450v2's are the quietest of the v2's.
V1 did not use switching power supply, they use discrete circuit and that is why they are a bit quieter

Hi, two things can cause the loud noise (humm).

The cables and the connection of power.

Cable can humm if it's not well fixed or the due to placing heavy object on it can cause damage to cables.Trouble shoot all cable by use a meter to read all cables( use the continuity function).

When a studio is not well connected in terms of power,you are likely to hear hum sounds.

Check the socket plugs and see if the earth wire is connected.That can cause hum too.

Good luck.