It might, but to be perfectly honest most people don't keep partitions of random-looking data, or large files containing what looks like it. Your plausible deniability would be of the form, "I was getting ready to make a hidden volume there, filled it with random bits etc., but I never got around to actually making it."

I'm not actually sure that TrueCrypt lets you separate these two aspects of creating a hidden drive, but Linux's tools do. With LVM (to create volumes in volumes) you could create a partition which exists within an encrypted partition, so that it's full with random data to begin with -- but then you could plausibly have forgotten to do anything with it after your computer was up and running.

Large random-looking files are a bit different; if someone were to ask "what's this 10 gig file of random data doing on your hard drive?" it would seem hard to answer them. The only thing that I know people use that much random data for is testing an RNG for its statistical properties.

Any good symmetric encryption algorithm produces data that looks random. You can't tell whether it's just noise or encrypted data.

I'd expect a sane judge to treat cases like these as circumstantial evidence — e.g. the police thinks that random data is really encrypted data, but has no proof. From what I know, it is difficult (though not impossible) to land in jail based on circumstantial evidence.

I guess if you use encryption tools that add unencrypted metadata headers (as in "this is a file encrypted using AES-256 in CBC mode"), then the evidence is stronger.

It's exactly the opposite: any random noise could be assumed to be encrypted data and therefore you can be jailed for being unable to decrypt the noise.