HI mrdistatty , welcome to the forum. There's a lot of things that could have occurred since the last time you used your Tandberg but if it was stored correctly (away from moisture, excessive heat etc). The first thing we need to determine is what this distortion sounds like and if there's anything that exacerbates it. You say that you installed a new drive belt so is it wow and flutter or electrical distortion?
One of the first things I do with an older deck is listen carefully to each channel on headphones and then listen to the deck itself. You may be well past this point but it bears mentioning for other folks. Checking out an old piece of gear thoroughly before you dive into it will give you a baseline. If someone were to ask you, "Did it sound like that before?". You should be able to answer that question with certainty. Of course, it'll be you asking that question. BTW, don't ask me if I always remember to do that! I sure have regretted not doing it before.
