possible cracked manifold?

dangtaco said:

alright so here it is...
whenever i'm driving on the freeway or on the street and getting to that time to shift, theres a very annoying ringing type sound coming from the front of the dash but in the engine bay on the driver side. could this be a cracked manifold? the sound is almost drowning out the sweet tune of my LC header

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Is it more ringing or whistling? Does happen at higher RPMs right before you step on the clutch to shift? Any change in power?
A good size leak in the intake manifold could cause a loud whistle type noise at higher RPMs. You can use WD-40, carb cleaner, or propane to check for intake leaks, spray a little around manifold and listen for rpms to increase without thouching the throttle. You can check for exhaust leaks when its cold by feeling around manifold for escaping air or use windex and it will blow bubbles if there is a leak. I say to do it when cold for 2 reasons, first and fore most you could burn yourself if hot and 2nd as it heats up, metal expands and could close small leaks making harder to find. Exhaust leaks tend to tick, intake leaks whistle.
Whether it be intake or exhaust leak you should notice a change in power.
Another thing it could possibly be is the pilot bearing in the flywheel for the input shaft of the transmission. I have heard them resonate thro the flywheel and bell housing and cause a ringing type noise at higher RPMs when bad.