How would you say it another way?
I couldn't help but notice that you've been packing.

....................................... that you've been packing.

Question

How would you say it another way?
I couldn't help but notice that you've been packing.

.......................................  that you've been packing.

Answer

I couldn't help but see that you've been packing. 
I noticed that you've been packing.

Answer

"I see that you've been packing."
"You've been packing, I see."
"Obviously/evidently you've been packing."
"It's obvious/evident that you've been packing."
"You've been packing, haven't you?"