You've almost located the problem!: what we found out, is an incompatibility between Tiger 10.4.11 (which is very close to the new OS Leopard) and Roxio 7.x I've read on other forums that Toast 7 is incompatile with Leopard - so that's the reason of the bug.
So how to solve it?
1. Go back to Tiger 10.4 using your installation CD (use the option install and archive)
2. Go to http://www.apple.com/support/downloads/mac...oupdateppc.html and dowload the 10.4.9 combo update (10.4.9 is the last "safe" update of Tiger as far as I know. Not so sure about 10.4.10, so in doubt, stick to 10.4.9).
You'll see the noise disappears. Yeeehaaa!!!
The quicktime version has no effect on Toast, but in case you also work with Final Cut, be aware that Quicktime 7.3.x is incompatible with Final Cut Pro HD 4.5... The last "safe" version of Quicktime to my opinion is 7.2 and it works just as fine.
All this makes me think that one should NEVER update automatically softwares - if your systems works fine, stick with the original versions as long as possible!!!