The Cambridge Grammar of the English Language (Huddleston and Pullum) says under the section "Past time could" at page 197 that it is possible to say
(1) I could hear something rattling. [actualised ability (says CGEL)]
but not possible to say
(2) * I could hear something rattle.
because rattle would be "perfective", says CGEL.
CGEL specifically says that "could does not normally appear in affirmative contexts when it is a matter of actualisation of a single situation viewed perfectively."
CGEL has another set of examples on this issue:
(3) Last night I heard the clock strike two. (marked grammatical in CGEL)
(4) * Last night I could hear the clock strike two. (marked ungrammatical in CGEL)
Now, here's a conversation from an American movie "Real Steel" (2011):
Max Kenton: Charlie, I need you to teach him to box.
Charlie Kenton: Are you kiddin' me? He's no where near advanced enough to handle Noisey's voice command.
Max Kenton: Yeah, so we need you moves, your commands. Start over.
Charlie Kenton: Forget it, kid.
Max Kenton: From the ground up.
Charlie Kenton: Forget it.
Max Kenton: You were a boxer Charlie.
Charlie Kenton: Yep.
Max Kenton: Yesterday at The Zoo, you could see things happen before they even happened.
Charlie Kenton: I haven't boxed in a long time, I'm not starting now.
Max Kenton: You can teach him to fight.
Charlie Kenton: You're doin' fine, Max. You don't need me, sorry.
How come it's not "you could see things happening" in the movie?
Is it some sort of BrE/AmE thing? Or is the movie script just being sloppy in its grammar?