Toro sw3200 Zero Turn Tractor squeaking

I have a Toro sw3200 zero turn tractor (the version with the steering wheel).  I have looked around the front end of the tractor, and the only lubrication points I see are on the front wheels themselves.  Yet when I am using the tractor, I get a squeaking noise from the front end.  I have lifted (somewhat) and tried spraying some lube, as there are a lot of moving parts for the front steering...  but I cannot seem to isolate the source of the squeaking or eliminate it.  Short of raising the front end and dousing it with a lubricant spray, can someone suggest anything to try? Of course an additional concern that I have is that if I spray everything with lubricant, I am sure that I will start getting buildup of clippings and debris under here.   
 
Additionally, I notice that the housing that holds the front wheels seems to come 'up through' the foot area, and there are little plastic caps on them.  I tried removing the plastic caps, but I cannot seem to do so.  I wasn't sure if perhaps there is something I can lubricate under this cap?  But again, I cannot seem to remove them, and am concerned about damaging something.  I am attaching a small schematic showing the area of the plastic caps.  
 
Appreciate anyone's suggestions here.  

Thanks for the reply.  The plastic caps seem soft and they spin freely, but damn, I couldn't pop either of them off.  I wasn't sure that I wanted to damage them by forcing them, but now knowing that they are made to come off, it helps me a lot.  I'll give that a look, as I am suspecting this could be a cause, or at least a part of the issue.  
 
I'll have to continue to look at the steering underneath as well, because doing some light spraying underneath helped.  But i have to be missing something.  Probably the wheel spindles themselves.  
 
 
 
 

SRTsFZ6
Looks like part #12 holds the assembly on:
 
 
 
As for the plastic cup atop the spindle, either pop it off (it will come off and go flying) or use a heat gun or hair drier to soften the plastic and pop it off easier.  
 
Once apart, just clean and grease the shaft, etc.   
 
.