What you’re hearing is clock noise from the delay ICs. There’s a trimpot that you can adjust to minimize the noise but if you really want to cancel it out you’ll need to replace it with a multi-turn pot.

Can you post a pic of the circuit board in your unit? I’ll try to mark the trimpot for you. DO NOT TOUCH ANY OTHER TRIMPOTS!

Here’s the marked pic. Do it this way:

Turn on the delay and have it plugged into an amp.
Turn the delay time to max.
Make a small mark on the circuit board with a Sharpie to mark where the trimpot is now set.
Use a small screwdriver to turn the trimpot back and forth while playing a single note and letting it delay. Turn your Blend to full delay, too.
You’ll hear the whistle come and go as you turn the pot back and forth. The correct setting, where the noise is at a minimum, is usually around the center of the trimpot’s travel. It’s a very fine adjustment so take your time with it until the noise is at a minimum with your delayed note.
Put it back together and play!

EDIT: set your delay control where you hear the most whistle and adjust it there. Then try it at full delay and make sure it’s acceptable there as well. You may neeed to readjust the trim.

There shouldn’t be any whistle on the clean sound as that’s not going through the delay circuit.

Have you tried adjusting the pot again on the clean signal? If it doesn’t change then the problem’s somewhere else.

Set the Blend where the whistle is loudest and try adjusting the trimpot.

Alsoooo… I was wondering if you all could recommend and mods or component upgrades for this particular unit. I was thinking about changing the input caps to silver mica and changing the smaller electrolytic caps (1uf) to metal film caps and the larger ones to tanatulum caps. And maybe upgrading the electrolyics to some nice sanyo or panasonic ones. Any recommendations would be greatly appreciated! I do like to go into pedals and take out all polarized electrolytics or at least the tone changing ones

Thanks Again,
Clay