Ressurecting a zombie-thread here.
I bought an MXR Bass Octave Deluxe last month while visiting the US. Came back to Norway and almost immediately after plugging it in I experienced the same issues as the OP posted; squealing, a distorted signal and at times random popping. I then e-mailed MXR who wrote back rather quickly (the day after) and told me to send it to them. I'll do this today and hopefully I'll get it back without having to wait too long.
Also, my MXR Bass Compressor crapped out this summer. I bought it used a couple of years ago, and this summer all the LED-lights were on the whole time. Since I bought it used I decided to send it to a local repairshop. It's gone two months and they're still waiting on parts.
So that's two MXR-pedals crapping out on me in two-three months. I do love their pedals and have had a Bass Envelope Filter and a Blowtorch that served me well for years. Also, I bought a Carbon Copy Delay at the same time I bought the Octave-pedal and it works fine.
So the the OP; how long did you have to wait?