Mine hasn't had any hum issues, and it kinda splits the difference between the Mark IV and a 5150 in some ways...which are my 2 favorite amps.
The Mark IVa has been the king around here for a couple of years now, though this one has given me a TON of headaches. Had to send it to mesa TWICE within a year. First, tried to take it to our local Mesa certified tech. They had it for 10 weeks, and could not fix it. Ended up shipping it out to CA, and got it back about 4 weeks later. Then about a month later, starts having the same exact issue, so it had to go back. I guess with these older ones, the Orange Drops start to fail. They replaced the failed ones the first time, but then others failed, and they ended up replacing all of them the second time. Wish they would've just replaced them all the first time, but oh well. So of the 2 years I have had it, it has worked for about 15 months LOL. Extremely frustrating...but it sounds so damn good!