Pixels Pulsing

Arrggh!!! Pardon me.

I have a project that's 1 hour, 45 mins long. Running it through compressor I get these weird pulses of blockieness/pixelization. Some of them look like bit rate spike kind of stuff with fast motion but others just happen at really odd times, with no fast motion. For instance, I have a scene where a woman is sitting talking to the camera and suddenly the image starts to pulse with blocks. It carries over briefly into the next scene, then dissipates. That kind of thing occurs throughout the video. I lowered the Max bit rate and it got better, but I'm a little worried about going too low.

Here's the weird thing - I've compressed it in the past - as drafts during the edit - and didn't have this problem.

It's standard DV, 720x480. I've compressed (lately) with a 2 pass VBR 5.0/ 6.0. Is that still too high? Doesn't seem like it should be.

Any help?

RJ Thomas