As Mercer and I are trekking through Snow Veil Sanctum he turns to me at one point and says "you're pretty noisy for one who claims to be a theif." I was rather gob smacked. He'd never said that before, and I can't imagine why he would say that. My sneak skill is at 87. Granted, I haven't taken the muffle perk or muffled my shoes. Haven't felt the need since I am wearing Linwe's armor which is extremely light. I can sneak right up on a Deathlord and get a sneak attack off before he wakes up. Seems to me Gallus has no right to talk about being noisy since he has the usual NPC MO of charging into battle the instant an enemy starts to search for us.

I suppose he might say this regardless, but I have never heard him say it before. Does it depend on whether you have take the muffle perk?

Edit: My bad, I meant Mercer Frey

That may just be dialogue that Mercer says to everybody regardless of their skillz. He's a first class @$$, he has no respect or regard for anyone, when he is ever anything but rude and dismissive? It would be perfectly in character for him to insult you under any circumstances. IIRC he had the same dialogue when I was doing that quest, and I was probably close to 100 in Sneak and wearing Muffle enchanted armor, and the one who kept giving away our position was him.

He's talking about your talking. To him, I mean.