@Speuc,
1a Current
optical problem (7) - I was guessing TROUBLE?
TOPICAL
17a Hitching a ride, Thurman ran off with Crosby (8) - (Uma, Bing...no idea haha)
THUMBING
25a Patterns in wood or sand (6)
GRAINS
28a
I rate cab poorly for being the source of infection (8)
BACTERIA