Small Block Chevy Screeching Noise when hot

confused: Recently installed a small block chevy 350 in my 1930 Model-A Hot Rod. The engine runs great as it has a Summit Cam with a slightly agressive grind, an Edelbrock 600CFM carb and the jugs are bored .060 over. Carb, water pump, alternator, fan belt, all new.
My Problem: After running for 50 or 60 miles the engine has developed a screeching sound after it warms up (5 or 10 minutes). It does not seem the noise is coming from the engine. Used all the recommended lubricants to break in the cam. The engine temperature is about 180f, and it has an electric thermal controlled fan. The noise almost sounds like a dry fan belt or an alternator/water pump berring - so I replaced both.
I've also checked the rockers, push rods, and inside the valve covers, and there's no interferrence.
When the car is idle the noise is very loud. As rpm's increase the nose is less pronounced. By touching the break peddle the nosie goes away. The noise seems to come from the passengers side of the vehicle near the starter area or the bell housing. The sound is very hard to isolate.
I plan on putting the vehicle on a lift over the next few days
to see if I can determine the root cause.
If there's any ideas if a hot-rodder has experienced this type of problem please advise.. thx

sounds like a vacuum leak at the carb base.....i had a 67 impala with a 70 vette 350 in it...it did the same thing...drove me nuts!!.....

"By touching the brake pedal, the noise goes away"....

Yep, vacuum leak....

From confused: Thanks for the information - I have verified it is a vacuum leak.
I'm not quite sure where the leak was coming from, but when
I replaced the filler plug with a new vented plug, the noise is gone.

Yes a few weeks ago I inadvertantly replaced the plug with a non-vented plug. Apparently there's a huge amount of vacuum in this engine with the new pistons and rings, the vacuum was sucking through what I believe was the bottom of the valve cover.