The description of the pass without trace spell says:
A veil of shadows and silence radiates from you, masking you and your companions from detection. For the duration, each creature you choose within 30 feet of you (including you) has a +10 bonus to Dexterity (Stealth) checks.
The description of tremorsense says:
A monster with tremorsense can detect and pinpoint the origin of vibrations within a specific radius, provided that the monster and the source of the vibrations are in contact with the same ground or substance.
Say a party of PCs has pass without trace active when they walk through a tunnel where an Umber Hulk has been waiting behind the wall in ambush for prey, using its tremorsense.
Does the Umber Hulk detect the PCs in spite of pass without trace because they are in contact with the floor?
Best Answer
Tremorsense doesn't negate Pass without Trace
Pass without Trace can help in stealth checks against the perception of a creature with Tremorsense.
Is stealth useful against Tremorsense?
The rules of Tremorsense only serve to state that a creature with that ability perceives the world through ground vibrations. What it doesn't do is give it a supernatural ability to perceive all movement around it automatically.
This means it still needs to pit its perception check against a hidden character's stealth check to perceive them, allowing a stealthy enough character to avoid detection.
(As pointed out by Chris Biasbas, this is backed up by Jeremy Crawford on Twitter)
Does Pass without Trace help against Tremorsense?
Pass without Trace says that "A veil of shadows and silence radiates from you[...]". Silence is the absence of sounds and sounds are vibrations. This means that Pass without Trace magically silences the vibrations creatures affected by the spell create. All of this considered it makes sense to rule that Pass without Trace helps in stealth checks against the perception of a creature with Tremorsense.