Check timing belt age

Look under the hood for a sticker indicating when the belt was changed. Lacking that you can use the inspection port to check for cracks or missing teeth.

On the simpler 2.2i or subsequent SOHC 2.5i the t-belt can easily be inspected for cracks or oil contamination. But the first-gen 2.5i DOHC OB motor is so friggin' fragile wrt internal HG high pressure failure (percolation) that the odds are that the HGs have already been replaced...along with its t-belt. Because of the DOHCs replacing the t-belt alone is NOT an easy job, as it's notoriously easy to get the belt one tooth off somewhere. There are special tools to prevent this occurrence. That said, this frail motor notoriously does NOT last much longer after a full HG job because of internal damage from chronic overheating in the past. Often a connecting rod will get so loose (and loud) that it'll detach and blow right through the block! Nasty stuff.... So before opening a rat's nest I'd just clean the tranny's ATF, switch to newer iridium spark plugs and ignition wires, add a new air filter and new serpentine belts (maybe that squeak is the idler pulley. Test by running ot only on the ps/alt belt. If quiet, then replace the idler along with the AC belt together. Buying ANY 1996-1999 2.5i DOHC OB or Legacy LS is a huge crapshoot. So in your case I would NOT follow GA's ordinarily-ok advice, and just let this sleeping bear alone except for the window dressing I mentioned. Keep the coolant and oil full and gather serenity where you can...and good luck! If for any bizarre reason you choose to replace the t-belt be sure to carefully perform a percolation test with a hydrocarbon sensor probe so that you don't have to replace the HGs and the t-belt all over again soon-after!! Owners HATE when that happens, and it was a routine disaster back in the day....