Hi Franco,
Many FT-101's have had their Carrier Crystals adjusted to match the aging crystal filter. A different white noise sound when switching from USB to LSB or vice-versa is the usual indication of a problem.
Please see the pdf located in our Files Folder #6 FT-101ZD Carrier Crystals Adjustment. Also good for the original FT-101 series.
73
Roger VE7LB
