I have a 1998 Civic ex. Sometimes when starting my car, mainly when its cold outside, it makes a high pitched squealing. USUALLY, when i get up past 2000rpm it goes away, but will come back when it again lowers below 2000rpm. I had a new alternator belt as well as a power steering belt (?) and was told they could just need tightening. Could it be something else?

SOURCE: Honda Odyssey EX 2001 - Power Steering Pump

Hi , aparentlyyour mechanic just dont want to check nothing else,any new noise should be checked before major damage may happens,the first noise sounds like the new timing belt is rubbing the cover because they removed the alternator and air conditioner belts to install the timing belt ,may be that they did not re install everything right the way it was.......

SOURCE: Honda accord 07 making a highpitched squeaking noise in cold

That Squeeling is your Belt. You may need a New Belt Tensioner to keep it Tighter. As a Quick fix, Go to your Auto Parts Store and get a Can of Fan Belt Dressing and spray this on the Belt and it will be Quite for a while. Please Rate my Solution, I need all the Help I can Get! Thanks!

SOURCE: 95 honda civic ex squeals when starting engine

Some of the grime, etc on the engine prior to steam cleaning along with any solvents used may have affected the drive/fan belt. I would suggest you either check tightness of the belt and possibly consider replacing it.

SOURCE: when backing up and sometimes

Your rear brake pads are most likely worn to the wear indicator which can make a high pitch squealing noise. It is very common that it will squeal when backing up, but not when applying the brakes. 50,000 miles is about the average life for rear brake pads on your car.

SOURCE: Motor Oil leaks from 1999 Honda Civic EX

make sure they are tight
could be time for head gaskets
make sure the old gasket from the old filter came off the block sometimes they come off old filter and stick this causes a leak due to improper seal.