Last week I made several contacts on my Icom 730 no problems. This week I have had several reports of being off frequency even though I was tuned in to their exact frequency and ssb b was set correct. I have made no changes to the radio and one report claimed I was transmitting about a 100 hertz high. What would cause this sudden change? The weather was dry last week and wet today, but I don't see if that would make any difference.