If you were to temporarily short the antenna the noise should disappear (almost completely) 80 meters is pretty noisy most places and could be made much worse of you are in an urban area with cheap power supplies, lights etc. I see that you are in India and depending on location you may have a great deal of offending electrical devices around.? The noise from the receiver would be on all bands if it is the ceramic filters. The test is might be to compare on different bands and perhaps listen to a friends radio, perhaps if they could set up at your QTH. I am lucky in that I have a good service monitor (IFR FM/AM 1200S) to check the signal to noise specs of a radio and be certain. Often people are quick to blame those ceramic filters for almost any problem on the FT-857 and they COULD be but not even the majority of the time. A quick comparison of your radio with another either at your QTH or another might clear up the issue.
