Chirping/squeal from engine
 

Just got 1989 2.5l. Have this annoying sound, previous owner had water pump and
Alternator switched. No coolant leaking onto belt and he says spark plugs not loose.
Apart from this car seems to run OK, drives well but doesn't start well in the cold. Alarm system also a pain, being set off by the slightest thing. It's really windy today so it keeps going off. Can it be disabled, or made less sensitive?
Hope someone out there has some other suggestions on the chirping noise, it's a real nuisance!

I would still check all the spark plugs. That is the cause of chirping most of the time.

Blacklight,
For the chirp/squeal - Inspect the big drive belt for the ancillaries. Look very carefully at the edges for fraying &/or dirt in the grooves.
If one edge of the belt is frayed, suspect that idler pulley bearings may be wobbly?
Use a stethoscope with the engine running to isolate the source? Careful!
Remove the belt entirely and run the engine briefly to hear if that eliminates the noise.
Place a straightedge across adjacent pulleys to observe their alignment. I found two of mine had new bearings but the bearings were slightly canted. This caused both idlers to wobble.Not good.

Remove the belt and run it for a few. See if still makes noise.

Despite assurances that plugs were the first thing checked. I put car into local performance car specialist. Spark Plugs!!!! Every single one loose and charred to a crisp!
Car now runs without squeal. My next question is creaking from steering? Car just passed UK MOT safety test ( compulsory). So I know it's safe to drive, however, steering creak is concerning me

Glad you found the cause of the chirping. I'm not sure about the steering noise.

Should say, I'm new to Porsche. Have AMG Merc as main car, and have previously owned Audi and Honda (never again!, too expensive to run for what you get. Honda that is!) Their bikes are excellent though but if it comes to two wheels, better to go BMW. My First Boxster is a 1998 2.5L and so far it's really been fun. Wife loves it.

My boxster made steering growling noises, the fluid level was not really low so I overfilled it with Pentosin and the noise went away. That was 8 years ago. Haven't heard it since.