Sniper rifles did not have silencers during World War II. Most sniper rifles of that era were not purposely design sniper rifles, but rather converted battle and hunting rifle. This made any attempts to suppress their noise difficult and especially considering the ammo used was full size supersonic rifle cartridges. For similar reasons silencing machine guns was not followed up and it is questionable whether that would offer any tactical advantage.
The Germans did not show much interest in silenced weapons, but the British Special Operation Executive did. they developed the Welrod pistol with an integrated silencer for use in assassinations by their operatives and agents. They also produced the best suppressed weapon, the De Lisle carbine. This was a specialist carbine and not a sniper rifle. it fired subsonic pistol ammunition (45 ACP ROUND) and had a effective range of (200 yards or 185 m) it's Maxium range was ( 400 yards or 365 m) a shot between 2 and 4 football fields long, not bad for the 45 m1911a1 pistol round but it was very quiet. It was used in a few covert SOE operations. So why add a silencer to a weapon that did not have silencers back in that time frame.