From what I've read it can be really problematic - have you always had it? At least my synaesthesia it not a problem at all - in fact I can't imagine how grey the world would seem without it.
Yup, I've always had it. I'm particularly sensitive to pops, clicks, and beeps. They don't need to be loud to be extremely off-putting.
The normal things in the house that beep (microwave, tumble dryer, etc) that beep when they're done drive me absolutely up a wall. If I'm running the dryer for a 20 minute cycle, for example, I can naturally tell when it's at about 18 minutes, and I'll go in and shut it off before it can beep. Sometimes I'll miss it, but not often.
It can be problematic to the extent that it's very startling when a noise like that goes off unexpectedly. Several years ago, MrsTasty got a new pair of prescription sunglasses, and the case was a spring-loaded one that snapped shut and made a little popping noise as it closed.
She'd just gotten them and I didn't know about the case, and she went to put them on while I was driving, snapped the lid shut, and it was such an unexpected noise, I drove off the road, down into the ditch, and nearly wrecked the car.
I've known several people with synesthesia, and they've all been in some kind of arts/creative career (musician, artist, designer, etc).