IRS called me and left me a automated message that warrant of arrest was issued. is this a scam? aren't they suppose to sent a letter?

That was a Scam and not from the IRS.  The IRS does not call taxpayers but only communicates through the US mail.

See this IRS website for phone scams - https://www.irs.gov/newsroom/irs-urges-public-to-stay-alert-for-scam-phone-calls

It's a scam.  The IRS will never call you.  They send correspondence.