All was ok with xorg 6.8. Starting from xorg7.0, the ati fans go to full speed when xorg starts, and go back to the right speed when it quits. Driver version of xf86-video-ati is 6.5.8.0. This bug does not occur when using ati proprietary drivers. I submitted this bug #7463 on bugs.freedesktop.org. As I don't know if something was rewritten for gentoo, please find it here too. Portage 2.1-r1 (default-linux/x86/2006.0, gcc-3.4.6, glibc-2.3.6-r4, 2.6.16-gentoo-r9 i686) ================================================================= System uname: 2.6.16-gentoo-r9 i686 Mobile Intel(R) Pentium(R) 4 CPU 3.20GHz Gentoo Base System version 1.6.15 app-admin/eselect-compiler: [Not Present] dev-lang/python: 2.4.3-r1 dev-python/pycrypto: 2.0.1-r5 dev-util/ccache: [Not Present] dev-util/confcache: [Not Present] sys-apps/sandbox: 1.2.17 sys-devel/autoconf: 2.13, 2.59-r7 sys-devel/automake: 1.4_p6, 1.5, 1.6.3, 1.7.9-r1, 1.8.5-r3, 1.9.6-r2 sys-devel/binutils: 2.16.1-r3 sys-devel/gcc-config: 1.3.13-r3 sys-devel/libtool: 1.5.22 virtual/os-headers: 2.6.11-r2 ACCEPT_KEYWORDS="x86" AUTOCLEAN="yes" CBUILD="i686-pc-linux-gnu" CFLAGS="-O2 -march=pentium4" CHOST="i686-pc-linux-gnu" CONFIG_PROTECT="/etc /usr/kde/3.5/env /usr/kde/3.5/share/config /usr/kde/3.5/shutdown /usr/share/X11/xkb /usr/share/config" CONFIG_PROTECT_MASK="/etc/env.d /etc/gconf /etc/revdep-rebuild /etc/terminfo /etc/texmf/web2c" CXXFLAGS="-O2 -march=pentium4" DISTDIR="/usr/portage/distfiles" FEATURES="autoconfig distlocks metadata-transfer sandbox sfperms strict" GENTOO_MIRRORS="http://distfiles.gentoo.org http://distro.ibiblio.org/pub/linux/distributions/gentoo" PKGDIR="/usr/portage/packages" PORTAGE_RSYNC_OPTS="--recursive --links --safe-links --perms --times --compress --force --whole-file --delete --delete-after --stats --timeout=180 --exclude='/distfiles' --exclude='/local' --exclude='/packages'" PORTAGE_TMPDIR="/var/tmp" PORTDIR="/usr/portage" SYNC="rsync://rsync.gentoo.org/gentoo-portage" USE="x86 X alsa apache2 apm avi berkdb bitmap-fonts cli crypt cups dlloader dri eds emboss encode esd f77 foomaticdb fortran g77 gcj gdbm gif gnome gpm gstreamer gtk gtk2 imlib ipv6 isdnlog java jpeg kde libg++ libwww mad mikmod motif mp3 mpeg ncurses nls nptl ogg opengl oss pam pcre pdflib perl png pppd python qt qt3 qt4 quicktime readline reflection sdl session spell spl ssl tcpd truetype truetype-fonts type1-fonts udev vorbis xml xmms xorg xv zlib elibc_glibc input_devices_keyboard input_devices_mouse input_devices_synaptics kernel_linux userland_GNU video_cards_radeon" Unset: CTARGET, EMERGE_DEFAULT_OPTS, INSTALL_MASK, LANG, LC_ALL, LDFLAGS, LINGUAS, MAKEOPTS, PORTAGE_RSYNC_EXTRA_OPTS, PORTDIR_OVERLAY
Yep, it's an upstream bug.