Two weeks ago I interviewed with a large company. The interview went well and I felt that the company would be a good fit for my needs. Some of the interviewers during the process seemed like they were impressed with my skill set and I walked away feeling pretty confident it would work out for everyone.
Earlier this week HR sent me a job offer with the request that I make a decision within a week. The pay didn't exactly blow me away but the benefits package is pretty good and it seemed like there was good opportunity for advancement. However, shortly afterwards I got an email from one of the current employees who interviewed me. (It was from his personal email, so I wouldn't have even realized it had he not had a memorable name). In this email he basically "warned" me against taking the job, saying that the company puts on a good face for interviews but is actually "soul-sucking" inside. He finished by complimenting my previous experience and telling me I shouldn't "shackle" myself to this company; to instead pursue "bigger and better things." For more background on this guy he was very nice/competent in the interview, looked about 10 years older than me, and works as a project manager in a department separate from but related to that of my offer.
This raises the question of not only whether I should take the job (lest it turn out to be a "trap" like this manager is saying) but also how I should treat this message. Should I tell the company that one of their managers is potentially sabotaging their hiring process, or just take his advice and walk away from the whole situation? I don't really see how this guy gains anything from me declining the job so it seems like he has genuine motives. On the other hand, I can hardly imagine the company is happy about this and would like to know.
What are my ethical obligations here?
How much stock should I put in this person's advice?