Do you mean he's speaking at a particular volume and then starts getting quieter? Hmmm.... I'd figure he doesn't want somebody eavesdropping on his conversation. Might be something perfectly innocent...Have you tried asking him why he drops his volume?
If he's changing the tone, then perhaps he is doing it (possibly subconsciously -- that is -- he's not aware he's doing it!) because he's interested in you. In which case, if you're curious, you might ask why he does it (but be prepared that he might not be aware he's doing it).
I'd interpret it as being sexy -- he's interested.
Because that's how we talk to girls. Be glad the man doesn't have a lisp or a squeeky voice. We don't try to its just natural. My girl thinks its sexy. This is because men have an adams apple it makes our voices lower & deeper then yours. =) ten points ?!=)
That means hes sexually attracted to you.
Throughout time girls have been more attracted to guys that are manly.
And its a subconsious act on his part. To seem more appealing to you
What were you guys talking about? Maybe he was with another woman and you were talking about something about your relationship he didn't want her to hear?