Anybody else got a problem with the dialouge being skipped?

I don.t remember when it started but alot of times in Halo Reach, someone won’t say say their line, such as when the portable bridge comes in in Tip of the Spear, Kat usually says nothing when I think she is scripted to says something like “Six protable bridge inbound, cross it to scout the next area”, normally she says it when I leave here behind to do something like what The Tyrant did in his LASO guide for Tip of thhe Spear, when I bring here with me, she doesn’t say it.
Occasionaly, when the seraph escort appears after cutting the engines of the corvette in Long Night of Solace, Dot woulld say “Warning, incoming contacts in the Aft Bay Quarter” before anyone says anything, sometimes she says it after everyone else speaks.
And recently, dialouge is being skipped, only happened once in Long Night of Solace, when Kat was drawing plans, her mouth moved, but nothing was said (And I heard Jun scratching his chin!).
In Halo 2, very rarely will somebody skip their line like in Reach, only in cutscenes though, and it mostly happened in the first cutscene of the level “Regret”.
Has this this happened to anybody else or maybe have a theory as to why this is happening?

Maybe your disc is scratched. It happened to me a lot before, then I took it out and cleaned it, now it works fine.