Inna, remember this, before you record, make sure there are no "fluorescent lights" within 100 miles. Demagnetize the heads, buy rubber cleaner for pinch rollers, buy new pinch rollers for whatever machine if possible, head cleaner of course. Demagnetize the heads after recording each tape. Make sure you're not thinking about anything else when you record. Recording LP's is a lot of precise work, and these suggestions are a big step in getting good results.
Good luck.