Do you experience lower sensitivity, to cracking noises and, usually both ?
Then check by changing the FM mode from Narrow to Wide (or versa) - if one
of the (usually acitive) modes is failing, then is seems the Ceramic Filter
has gone SK !
In many rigs, the schematic diagram shows that the diode DC switching voltage (FM-W to FM-N) is applied to the ceramic filter, although the manufacturer's data sheet says that a DC blocking capacitor should be used. The problem is not the filter, it's that the rig design overlooked the need to avoid applying DC voltage to the filter ... The result is slow degradation over time, either the receiver goes deaf, or it develops a case of the crackles because some 'salt crystals' (so called 'dendrites') are growing in the filter due to electromigration.
You can replace the CF, but after some time, problem will re-appear ... How to cure the trouble once and for all ? You can avoid DC voltage reaching the CF simply by inserting a blocking capacitor (1nF ... 10nF) in line. There are some mods published on the Internet where the PCB tracks must be interrupted / cut and bridged, but this is quite a risky job on the densely populated TM-D710 PCB.
If you are working on the CF, it is wise to replace them all four in one time. See info about filter types and PCB locations here. You can buy them as spare parts from Kenwood or through various on-line shops, the price is a couple of EUR. The 'G' type is for N-FM (+/_ 4,5 kHz), the 'E' type is for W-FM (+/_ 7.5 kHz).
After removal of all filters, prepare the PCB by cleaning the PCB solder pads, and adding/applying solder to fill the through holes completely. Then the 8 pces SMD capacitors ( 1 .. 10 nF types) can be mounted as 'studs'. Finally mount the CF, I had to cut about 1mm from their leads for a nice fit.. Do not forget to solder the 3 'ground' leads/terminal as well, you will need a long tipped soldering iron to go underneath the CF. For adding some mechanical strength, I applied some (white) silicon glue in between filters.
As a picture tells more than 1.000 words, see below !